(a) Field of the Invention
The present invention relates to device and method for manufacturing a wheel bearing assembly. More particularly, the present invention relates to device and method for manufacturing a wheel bearing assembly that reduces an error rate by reducing stress concentrated on rolling elements in manufacturing processes of the wheel bearing assembly.
(b) Description of the Related Art
Generally, a wheel bearing assembly rotatably connects a wheel to a vehicle body and enables a vehicle to move. Such a wheel bearing assembly is divided largely into a driving wheel bearing assembly that transmits torque generated in an engine and a driven wheel bearing assembly that does not transmit torque.
The driving wheel bearing assembly includes a rotatable element that is rotatably connected to a driving shaft that is rotated by the torque generated in the engine and transmitted from a transmission so as to rotate together with the driving shaft, and a non-rotatable element fixed to the vehicle body. Rolling elements are interposed between the rotatable element and the non-rotatable element. The rotatable element of the driven wheel bearing assembly is not connected to the driving shaft, but other components of the driven wheel bearing assembly are the same as those of the driving wheel bearing assembly.
For stable performance, the wheel bearing assembly is manufactured such that a preload is applied to the rolling elements. An orbital-forming method is mainly used for applying preload to the rolling elements.
A conventional orbital-forming method will be briefly explained.
Firstly, a first row of rolling elements is inserted on the rotatable element of the wheel bearing assembly (hereinafter referred to as a “hub”), and an outer ring is mounted such that the first row of the rolling elements is contacted with first inner and outer raceways. After that, a second row of rolling elements is inserted on the second outer raceway and an inner ring where a second inner raceway is formed is press-fitted to the hub. At this time, an end portion of the hub is protruded from the inner ring in an axial direction thereof.
At this state, the wheel bearing assembly is located such that the end portion of the hub faces upwards, and the hub and the outer ring are fixed to a base so as to not move.
After that, the end portion of the hub is pressed downwardly by a forming tool that is slanted with respect to a hub axis (that represents a central axis of the wheel bearing assembly) at a predetermined angle and rotates about the hub axis. In this case, the end portion of the hub undergoes plastic deformation and is deformed radially outwardly toward the hub. At this time, the inner ring applies a preload to the rolling elements and is axially fixed.
However, since a difference of rotational speed between the forming tool and the hub is large according to the conventional orbital-forming method, the forming tool imparts a large impact on the end portion of the hub the moment that the forming tool contacts the hub. Particularly, since the end portion of the hub has a thinner thickness compared with other parts of the hub, the end portion may be broken by such a large impact.
In addition, stress is concentrated on the rolling elements as a consequence of impact that the forming tool imparts to the hub. However, since the outer ring is fixed according to the conventional orbital-forming method, such stress concentration on the rolling elements cannot be reduced.
Such stress concentration on the rolling elements increases an error rate of the wheel bearing assembly.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.